A false-twist apparatus, as for example described in commonly owned U.S. Pat. No. 4,226,080 or in copending U.S. application Ser. No. 182,649, filed Aug. 29, 1981 has a support which defines three generally parallel and radially spaced axes which surround a central axially extending twisting region. Respective shafts lie on these axes and are journaled in the support for rotation about the respective axes. Respective axially staggered sets of axially spaced disks are fixed on the shafts with the disk rims normally radially overlapped at the twisting regions. A pair of yarn eyes axially flank the disks and are axially aligned with the twisting region so that a yarn to be false-twisted can pass axially through one of the eyes, then zig-zag along the region in contact with the disks, and then pass axially through the other eye. The shafts and the respective disks are all jointly rotated in the same direction, in one direction for S-twisting the yarn and in the opposite direction for Z-twisting the yarn.
Switching between S-twist and Z-twist is not a simple matter of reversing rotation direction for the disks assemblies each constituted by a shaft and the respective disks. It is also necessary when switching between S-twist and Z-twist to change the order of the disks, so that the helix along which the yarn passes as it zigzags through the twisting region will also be reversed. Thus it has been suggested in German printed patent application No. 2,213,147 to mount the disks releasably on the respective shafts. Thus in order to switch the S-twist and Z-twist all of the disks must be removed from the respective shafts and the disks from one shaft switched with the disk of another shaft. Since in a typical texturing installation 200 such false-twist devices may be provided, this represents an enormous amount of work. In fact a machine can be down for a day or more for switching between S-twist and Z-twist.
German utility model No. 7,434,582 shows another arrangement wherein these assemblies can be moved relatively easily from their respective shafts so that they can be switched around for converting from S-twist and Z-twist. With such an arrangement it is therefore necessary to loosen three screws and then removed all three of the disk assemblies so that two of them can be switched with each other. Such an operation is also relatively laborious.
It is also been suggested in German published patent application No. 2,310,802 of W. J. Morris and D. L. McNeight to provide an arrangement wherein one of the disk assemblies can be moved from mesh with one side of the other two disk assemblies to the other side of these assemblies, thereby moving over the twisting region. Such an arrangement therefore requires a relatively complex drive system for the two fixed disk assemblies and the one movable disk assembly, as well as complex bearing structure. What is more, the conversion between these different types of twist also moves the twisting regions so that the guide eyes must be appropriately repositioned.